The central nervous system (CNS) includes the brain, the brain stem, and the spinal cord. The CNS is isolated from the external world by several membranes that both cushion and protect the brain, the brain stem, and the spinal cord. For example, the membranes that form the blood-brain barrier (BBB) protect the brain from certain contents of the blood. The blood-cerebrospinal fluid barrier (BCSFB) protects other portions of the CNS from many chemicals and microbes.
Traditional methods for delivering compounds to the CNS are typically invasive. For example, a pump implanted in the skull, such as an intracerebroventricular pump, can deliver a variety of compounds to the brain. However, implanting such a pump requires brain surgery, which can entail a variety of serious complications. Certain compounds, for example epidural painkillers, can be injected directly through the protective membrane into the CNS. However, such injection is impractical for most compounds.
Intranasal administration has traditionally focused on the distribution of drug solutions as a mist for topical delivery to the nasal epithelium. Because of the nasal cavity's easily accessed vascular bed, nasal administration of medications has focused the delivery of medications either locally to the nasal cavity or directly to the blood stream.
Much of the current brain research is focused on the enhancement of the drug being delivered to the brain by various formulations. The traditional approaches to improve uptake of compounds to the brain by formulation enhancement include (1) mucoadhesive formulations; 2) penetration enhancers; 3) liposomes; 4) vasoconstrictors; and 5) nanoparticles. Examples of various compounds with have enhanced formulations include various cytokines, for example, tumor necrosis factors, interleukins, and interferons discussed in U.S. Pat. No. 6,991,785 and growth and differentiation factor-5 (GDF-5) and related proteins discussed in US Publication No. 20100074959.
Targeting of drugs to the central nervous system (CNS) is a challenging task. A great number of drugs, including biotechnology products, are candidates for treatment of CNS diseases, but drug delivery is a problem for brain targeting. A limitation in the treatment of brain tumors is that less than 1% of most therapeutic agents administered systemically are able to cross the BBB. The transport of small molecules across the BBB is the exception rather than the rule, and 98% of all small molecules do not cross the BBB (Pardride, NeuroRx. 2005 January; 2(1): 1-2. 2005); approximately 100% of large-molecule drugs or genes do not cross the BBB (Pardride, NeuroRx. 2005 January; 2(1): 1-2. 2005). The BBB allows small (about less than 500 Da), lipophilic molecules from the bloodstream to enter the CNS (Pardridge, Arch Neurol. 2002; 59:35-40). Many larger therapeutic agents are prevented from reaching the brain for treating CNS disorders such as but not limited to Parkinson's disease, Alzheimer's disease, depression, stroke, and epilepsy (Pardridge, NeuroRx. 2005 January; 2(1): 3-14). Disorders including autism, lysosomal storage disorders, fragile X syndrome, ataxis, and blindness, are serious disorders where there is little effective treatment. In many of these cases, the gene underlying the disease is known, but BBB delivery is the rate-limiting problem in gene therapy or enzyme replacement therapy, and no therapeutics have been developed. Drug delivery of therapeutic compounds, for example proteins, faces several challenges because of their instability, high enzymatic metabolism, low gastrointestinal absorption, rapid renal elimination, and potential immunogenicity.
There is a need for devices that can deliver compounds to the upper nasal cavity for direct nose-to-brain delivery. Certain existing nasal drug delivery devices do not adequately propel the drug from the device. Inconsistent propulsion of drug due to inconsistent user actuation is also far from optimal. Still further, the plume generated by such existing devices is too wide. Even further, some drug products do not readily mix and/or stay suspended with propellants in a MDI type device. Certain existing nasal drug devices rely on circumferential velocity to propel medicaments to the olfactory epithelium. Traditional circumferential devices result in a lower percentage of compound deposited on the olfactory epithelium. A circumferential component in the aerosol plume tends to result in a wider spray plume with a portion of the aerosol particles targeted to the sides of the nasal cavity in the lower part of the nasal cavity.
Better mechanisms for administering desired agents to the brain, brain stem, and/or spinal cord are needed.